A while back we published an article explaining the support constraints that surrounded deploying Exchange 2007 with multiple Outlook Web App (OWA) Virtual Directories (see here http://msexchangeteam.com/archive/2008/01/07/447828.aspx) and as this idea seems to come up more and more frequently, we wanted to do the same for Exchange 2010.
Microsoft supports using multiple OWA and Exchange Control Panel (ECP) virtual directories on a single Exchange 2010 Client Access Server, each in its own website. Each virtual directory must be listening on the standard port (TCP 443) for the site.
NOTE: You must ensure that the Default Web Site is set to All Unassigned for IP, or problems will occur with PowerShell.
You Had Me At EHLO... : Configuring Multiple OWA/ECP Virtual Directories on Exchange 2010 Client Access Server
Please read the full article . . .